Due to users' demand for an increasingly high rate of wireless access, there emerges the WLAN, which is able to provide high-rate wireless data access in a relatively small area. Various techniques have been used in WLAN, among which a technical standard with more applications is IEEE 802.11b. This standard involves the frequency band of 2.4 GHz with a data transmission rate up to 11 Mbps. Other technical standards involving the same frequency band include IEEE 802.11 g and the Bluetooth, where the data transmission rate of IEEE 802.11 g is up to 54 Mbps. There are other new standards such as IEEE 802.11a and ETSI BRAN Hiperlan2 which use the frequency band of 5 GHz with the transmission rate up to 54 Mbps as well.
Although there are various techniques for wireless access, most WLANs are utilized to transfer IP data packets. The specific WLAN access technique adopted by a wireless IP network is usually transparent to the upper level IP. Such a network is usually configured with Access Points for implementing wireless access of a user terminal and implements IP transmission with network controlling and connecting devices.
Along with the rising and developing of WLAN, the focus of research is shifting to the inter-working of WLAN among various wireless mobile communication networks, such as GSM, CDMA, WCDMA, TD-SCDMA, and CDMA2000. In accordance with the 3GPP standards, a user terminal is able to connect to Internet and Intranet via the WLAN access network and also connect to the home network and visited network of a 3GPP system via the WLAN access network. To be specific, when accessing locally, a WLAN user terminal, like WLAN user equipment (UE), will get connected to the 3GPP home network via the WLAN access network, as shown in FIG. 2; when roaming, it will get connected to the 3GPP visited network via the WLAN access network. Some entities of the 3GPP visited network are connected with corresponding entities of the 3GPP home network, for instance, the 3GPP Authentication, Authorization, Accounting (AAA) proxy in the visited network is connected with the 3GPP AAA server in the home network, the WLAN Access Gateway (WAG) in the visited network is connected with the Packet Data Gateway (PDG) in the home network, as shown in FIG. 1. FIG. 1 and FIG. 2 are the schematic diagrams illustrating networking architectures of a WLAN inter-working with a 3GPP system with and without roaming, respectively.
As shown in FIG. 1 and FIG. 2, a 3GPP system primarily comprises Home Subscriber Server (HSS)/ Home Location Register (HLR), 3GPP AAA Server, 3GPP AAA Proxy, WAG, PDG, Offline Charging System and Online Charging System (OCS). WLAN user terminals, WLAN access network, and all the entities of the 3GPP system together constitute a 3GPP-WLAN inter-working network, which can be used as a WLAN service system. In this service system, 3GPP AAA Server is in charge of the authentication, authorization, and accounting of a subscriber, collecting the charging information sent from the WLAN access network and transferring the information to the charging system; PDG is in charge of the transmission of the user's data from the WLAN access network to the 3GPP network or other packet networks; and the charging system receives and records the users' charging information transferred from the network. OCS instructs the network to transmit the online charging information periodically in accordance with the expense state of the online charged users and makes statistics and conducts control.
Under the non-roaming condition, when a WLAN user terminal desires to access directly to the Internet/Intranet, the WLAN user terminal can get access to Internet/Intranet via WLAN access network after it passes authentication and authorization of AAA server (AS) via WLAN access network. Should the WLAN user terminal desire to get access to the service of 3GPP packet switching (PS) domain as well, it may further request the service of Scenario 3 from the 3GPP home network. That is, the WLAN user terminal initiates a authorization request for the service of Scenario 3 to the AS of the 3GPP home network, which will carry out service authentication and authorization for that request; if it succeeds, AS will send an access-accepted message to the WLAN user terminal and assign a corresponding PDG for the WLAN user terminal. When a tunnel is established between the WLAN user terminal and the assigned PDG, the WLAN user terminal will be able to get access to the service of the 3GPP PS domain. Meanwhile, the CGW/CCF and the offline charging system (OCS) record the charging information in accordance with the WLAN user terminal's using state of the network.
Under the roaming condition, when a WLAN user terminal desires to get access directly to the Internet/Intranet, it may make a request to the 3GPP home network by way of the 3GPP visited network for access to the Internet/Intranet. Should the WLAN user terminal also desire to request the service of Scenario 3 to get access to the service of the 3GPP PS domain, the WLAN user terminal needs to initiate via the 3GPP visited network a service authorization procedure at the 3GPP home network. The authorization is carried out likewise between the WLAN user terminal and AS of the 3GPP home network. After the authorization succeeds, AS assigns the corresponding home PDG for the WLAN user terminal, then the WLAN user terminal will be able to get access to the service of 3GPP PS domain of the home network after it establishes a tunnel with the assigned PDG via the WAG of the 3GPP visited network.
At present, however, the international specifications define for a WLAN operating network only the procedure of establishing a service tunnel between a user and a PDG while needed. There has been so far no specific solution put forward to release a service tunnel and terminate the service when the use of the tunnel is over or when the tunnel has to be released due to certain special reasons.